Ok, so due to ususal codex edginess, and the fact that the older game must always be better than the new game, because nostalgia fags. Let's look at what this game does worse and what it does better than DS1.
Better than DS1.
-Gameplay. There is just no discussion to be had here. Gameplay wise, DS2 is superior to DS1 by bringing in subtle but game changing modifications that improved the gameplay all over the board. Game exploits like infinite backstabs in PVE has pretty much been dealth with, infinite blocking is no longer a viability, and dodging must actually be considered, rather than spastically side rolling every fucking time. What's more, the non-boss monsters and the environmental dangers are just waaaaaaaaaaaaaaaaaaay better in DS2. In DS1 the game relied on killing you almost exclusively by knocking you off, or making you fall off thin ledges, that was the only way they tried to kill you pretty much. In DS2, not the case at all, there are way more traps, there are ambushes, and cleverly designed monsters that pose real danger.
-This is my personal opinion, and probably controversial, but I liked the NPCs more in DS2. In DS1, they relied to much on the NPCs being either alice-in-wonderland-ish or having that creepy laughter, or just being plain evil. Pate has been said to be just another patches, which in my opinion is bullshit. Patches was completely one dimensional, and you knew what he was doing, Pate? Not so much. In fact, playing through I have realized that you have no evidence to whether he is tricking you or not. He is much more interesting and open to interpretation than Pathces ever was, and really, the only thing you have to go on, that he's setting you into traps, is anecdotal evidence from other NPCs who claim to have known that he set them up. What's more, Pate also helps you in fighting the last Giant. And since not everything has to be grimdark, both DS1 and DS2 also had humorous characters, but again, DS2 just outwits DS1 here. Gavlan and Straid (which has the same voice actor I guess as Frampt, but much better use of the voice) are just some of the most memorable characters I've ever seen, and both made me grin wildly.
-And speaking about humor, the statues that you can throw on the ground that say "hello", "thank you", "I'm sorry" and "very good", fucking pure gold! And also very useful in conveying information you can't easily do with gestures.
-Bigger game, this can be listed as both a con and pro, I guess.
-Way better matching making, it actually works this time around, unlike DS1, where you could never make a connection.
-Better looking game, technically.
-Better, more interesting covenants.
Worse than DS1:
-Less interconnectivity, it seems to be the case. There are at least 3 points that I remember, where you can progress no further, and must warp back to majula. (Now that I think about it, DS1 actually had at least 3 points where you could continue no longer as well, and you just had to warp back, hmm, I'm not sure if this is actually true)
-Has more ugly areas, lost bastille is particularly a sore point here in my opinion. Of course the dragon shrine and the zone leading up to it, is more beautiful than anything previously seen in From games. Truly marvelous.
-Some areas, particularly the gutter and iron keep are very gamey, and doesn't have the organic feel that many areas in DS1 had. This is a consequence of the ramping up on the gameplay, and making more interesting environmental dangers by making gauntles, but it's still a pity that they couldn't do it in a better way. Most other areas do feel as organic as DS1 though.
-Less varied boss fights? I'm not sure about this. DS2 has way more boss fights, so they may seem more samey, but I think they don't have that much less variety. I have to think about it some more.
-Extreme rarity of twinkling titanite. This would be understandable, if these weapons were much better than the one requiring the normal titanite, but they aren't. It strongly discourages experimentation, and forces you to consult wikis on whether it will be good or not, which sucks. This is actually my single biggest gripe with DS2 with respect to DS1.
Anyway, obviously my list is biased, disclaimer, but anyone saying that DS2 is a failure is as a sequel is a retard. It's an extremely worthy sequel, and not what fallout 2 was to fallout 1 at all.